Lor San Tekka mentions “balance in the Force” in the very first scene of TFA.
The existence of the Jedi temple on Ahch-To in TLJ furthers the prequels’ idea of Jedi temples being a thing.
We get to see Mustafar in TRoS, we even see its gas giant in the first shot.
In TRoS, Palpatine repeats his line about the dark side from the opera scene from RotS.
The Jedi voices and the Nubian starfighters in the climax of TRoS.